This invention has been developed primarily for use in the manufacture of pallets and building panels, using rice husk or hull. Accordingly, the invention will be described primarily in relation to these applications and this material. It will be appreciated, however, that the invention is not limited to these particular fields of use.
One application for structural panels is in the construction of pallets which, as is well known, are widely used for the storage, transportation and handling of bulk materials. The vast majority are formed from timber planks and beams nailed together to define a generally planar support surface and longitudinal channels adapted for engagement by forklift tynes. A major problem with such panels, however, is that the nails tend to work loose over time as a result of timber shrinkage, impact damage, general wear and tear, and misuse. Once the nail heads begin to protrude, bagged products such as grain and other commodities begin to be subjected to unacceptable damage. This renders the pallets effectively unusable, without costly maintenance and repair. Timber pallets are also prone to splintering, which gives rise to similar problems. A further problem with wooden pallets is that in wet environments, the wood can rot, or worse still, provide a damp environment in which harmful bacteria can breed.
In an attempt to overcome these difficulties, particularly in the food industry, plastic moulded pallets have been used. It has become apparent, however, that such pallets will not withstand the heavy duty cycle to which they are inevitably subjected. In an attempt to overcome this problem, reinforced plastic pallets have been produced with multiple strengthening webs and ribs. However, these are subject to a further disadvantage in that the numerous additional recesses and crevices defined between and around the strengthening webs are difficult to clean effectively, and hence allow fungi and bacteria to thrive. Again, this is particularly disadvantageous in the food industry. As a further alternative, metal pallets have been produced. However, it has been found that in order to provide the necessary structural integrity, the weight becomes excessive and/or the cost commercially unviable.
In view of the above, there remains a long felt need for a pallet with a substantially smooth, continuous support surface, which is formed without nails, is easy to clean, is repairable, and which has a heavy duty service capability.
Another application for structural panels is in the field of housing construction. In conventional building techniques, the walls are normally constructed by first erecting a timber frame. The frame is normally clad internally with a suitable laminate material such as plasterboard whilst the external walls are normally formed from weatherboard, brick veneer, or other more contemporary cladding materials such as aluminium sheeting.
These conventional techniques are relatively labour intensive and costly, partly because workers from numerous specialised trades are required. These include builders, carpenters, brick layers, joiners, plasterers and the like, all of which add to the overall cost. A further disadvantage is that these construction techniques consume relatively large quantities of valuable and diminishing resources, especially timber, which are progressively increasing in cost as supplies become less available. A further disadvantage is that conventional housing construction techniques require the vast majority of the construction work to be conducted on site, by skilled labour. There is little scope for initial prefabrication or modular construction and minimal scope for modifying or restructuring a house in a cost-effective manner, once built. Moreover, in the event that a house needs to be demolished or relocated, there is minimal scope for recycling or reusing the constituent materials, which in such circumstances are largely wasted.
All of the above problems are particularly significant in developing countries where the availability of skilled labour is limited and the cost of conventional building materials is often prohibitive. In an attempt to ameliorate some of these problems, various low cost building materials have been developed, such as fibre reinforced cement (FRC) sheeting which can be applied, relatively easily, to a timber framing structure. However, this form of construction gives rise to a "flimsy" subjective impression which is often seen as undesirable compared to brick construction, which gives the impression of solidity. The insulation properties are also minimal, which often necessitates an intermediate layer of insulation in the wall cavity, further adding to the overall cost. Moreover, because the cladding sheets have minimal structural integrity, the conventional framing structure is still required.
In a further attempt to address these problems, the use of composite panels has also been proposed. Panels of this type typically incorporate a series of laminates fabricated from different materials designed to achieve the desired strength to weight characteristics, as well as to provide thermal and acoustic insulation properties. A major problem with known fabrication techniques, however, is that there is a practical limit to the maximum length of the individual panels. This in turn leads to the requirement for smaller panels to be joined end to end to form a combined panel assembly of the necessary size. Typically, however, inadequate techniques for joining the panels have resulted in such structures being relatively weak. The resultant loss of structural integrity has, in turn, resulted in the potential strength characteristics not having been realised in larger scale applications particularly housing. For this reason, composite panels have tended only to be used to form internal partitions and non-load bearing walls, where significant structural integrity is not required. Accordingly, a separate framing structure is still required and the inherent problems associated with conventional building methods have remained largely unsolved.
In view of the above factors, there remains a long felt need for a cost-effective alternative to existing housing construction techniques, which would provide an alternative to the diminishing supplies of raw materials, require less use of skilled labour particularly on site, would lend itself to prefabrication, and which would be modular to some extent so as to allow the flexibility for structures to be built, altered or moved as required at minimal additional cost.
The present invention relates to the manufacture of structural panels and associated products using waste organic material, and in particular rice hull. Each year in Australia and around the world, the processing of rice for human consumption involves the removal of millions of tonnes of rice husks or "hulls". These hulls are particularly difficult to dispose of, because, being formed substantially of lignin, they are essentially waterproof and resistant to biodegradation. Furthermore, the relatively high silicic acid content limits their use as cattle fodder. Even rodents and insects will not consume them.
One means of disposal is to incinerate the hulls at high temperature, which substantially reduces their volume. However, this process is relatively energy inefficient, expensive, and has undesirable effects on the environment, particularly in terms of atmospheric pollution. Due to the difficulties of disposal, some attempts have also been made to use waste rice hulls and similar organic waste materials constructively. They have, for example, been used as insulation in building cavities and other applications. However, this use has hitherto been severely limited due to the lack of structural integrity of the raw material. In an attempt to address this problem, rice hulls have also been mixed with various binding agents. For example, it has been known, although not commonly, to employ a binding agent curable by RF (radio frequency) radiation in order to consolidate the individual rice hulls. However, this has also been found to be an expensive process which is not generally cost effective on a commercial scale. Moreover, to date, the products from this and other techniques have been excessively weak and prone to crumbling. More particularly, they have lacked the requisite structural integrity for use as a self-supporting structural material, which has substantially limited their applicability in many potential fields of use, including the building industry.
In view of the above, it will be appreciated that a process capable of forming a structural product using waste rice hull would address the significant problem of waste disposal, whilst at the same time providing a useful and commercially viable alternative to the diminishing supplies of raw building materials, particularly timber. To date, however, no such process or product has been found.
It is an object of the present invention to overcome or substantially ameliorate at least some of the disadvantages of the prior art.